Information storage devices are used to retrieve and/or store data in computers and other consumer electronics devices. A magnetic hard disk drive is an example of an information storage device that includes one or more heads that can both read and write, but other information storage devices also include heads—sometimes including heads that cannot write. For convenience, all heads that can read are referred to as “read heads” herein, regardless of other devices and functions the read head may also perform (e.g. writing, flying height control, touch down detection, lapping control, etc.).
In a modern magnetic hard disk drive device, each read head is a sub-component of a head gimbal assembly (HGA). The read head typically includes a is slider and a read/write transducer. The read/write transducer typically comprises a magneto-resistive read element (e.g. so-called giant magneto-resistive read element, or a tunneling magneto-resistive read element) and an inductive write structure comprising a flat coil deposited by photolithography and a yoke structure having pole tips that face a disk media.
The HGA typically also includes a suspension assembly with a laminated flexure to carry the electrical signals to and from the read head. The read head is typically bonded to a tongue feature of the laminated flexure. The HGA, in turn, is a sub-component of a head stack assembly (HSA) that typically includes a plurality of HGAs, a rotary actuator, and a flex cable. The plurality of HGAs are attached to various arms of the rotary actuator, and each of the laminated flexures of the HGAs has a flexure tail that is electrically connected to the HSA's flex cable.
The position of the HSA relative to the spinning disks in a disk drive, and therefore the position of the read heads relative to data tracks on the disks, is actively controlled by the rotary actuator which is typically driven by a voice coil motor (VCM). Specifically, electrical current passed through a coil of the VCM applies a torque to the rotary actuator, so that the read head can seek and follow desired data tracks on the spinning disk.
However, the industry trend towards increasing areal data density has necessitated substantial reduction in the spacing between data tracks on the disk. Also, disk drive performance requirements, especially requirements pertaining to the time required to access desired data, have not allowed the rotational speed of the disk to be reduced. In fact, for many disk drive applications, the rotational speed has been significantly increased. A consequence of these trends is that increased bandwidth is required for servo control of the read head position relative to data tracks on the spinning disk.
As the density of the data tracks increases, a microactuator may be employed in combination with the VCM to improve the tracking performance of the servo system. Some of these designs utilize one or more piezoelectric (PZT) microactuators that are affixed to a stainless steel component of the suspension assembly (e.g. the mounting plate or an extension thereof, and/or the load beam or an extension thereof, and/or an intermediate stainless steel part connecting the mounting plate to the load beam). Any suitable microactuator may be employed, such as a PZT actuator.
Some two element PZT microactuators include a first PZT element of a first polarity and a second PZT element of a second polarity. Occasionally, unbeknownst to the suppliers thereof, microactuators are shipped with both PZT elements of the same polarity. Such defective same polarity two PZT element microactuators are otherwise indistinguishable from non-defective, different polarity two element microactuators during the high volume manufacturing processes. The defectiveness of the same polarity microactuators only becomes apparent when the drive fails to operate, whereupon it is discovered that the drive fails to operate because the microactuator has effectively zero stroke; that is, it cannot move or respond appropriately to applied voltage. Such defective drives are costly and decrease the yield of the high volume manufacturing process.